/Engine/Plugins/Experimental/PCG/Source/PCG/Public/Elements/Metadata/PCGMetadataOpElementBase.h
WhenSignaturedoesn't have any templated types anymore (Signature<>), we got all our input values packed in "InArgs", so it's time to compute our operation and set the outputs. To do so, we use Apply templated with the LastOutputIndex, and go backwards (last output to first output).
namespace PCG { namespace Private { namespace NAryOperation { template<typename... Callbacks, typename... Args> bool PCG::Private::NAryOperation::Gather ( [FPCGMetadataElementBase::FOperationData](API\Plugins\PCG\Elements\Metadata\FPCGMetadataElementBase\FOperationData) & InOperationData, int32 StartIndex, int32 Range, const [Options](API\Plugins\PCG\Elements\Metadata\Options) & InOptions, const [TTuple](API\Runtime\Core\Misc\TTuple)< Callbacks... > & InCallbacks, int InputIndex, [Signature](API\Plugins\PCG\Elements\Metadata\Signature)<> S, Args &&... InArgs ) } } }